U.S. patent number 5,913,854 [Application Number 08/794,803] was granted by the patent office on 1999-06-22 for fluid cooled ablation catheter and method for making.
This patent grant is currently assigned to Medtronic, Inc.. Invention is credited to Joseph M. Karratt, Hong Li, Mark A. Maguire, Aurelio Valencia.
United States Patent |
5,913,854 |
Maguire , et al. |
June 22, 1999 |
Fluid cooled ablation catheter and method for making
Abstract
A catheter assembly (2) includes a catheter shaft (6) having a
tip portion (10) with a hollow interior (30) and a linear ablation
electrode (18, 34, 36, 44, 58) spaced apart from the distal end
(22) of the tip portion. The electrode has an inner surface (28)
which is effectively fluidly exposed to the hollow interior so that
a cooling fluid (32) passing through the interior contacts the
inner surface so to effectively cool the electrode. The electrode
can include a series of band electrodes (18, 34) or one or more
spiral electrodes (36, 44, 58). One method for making the tip
portion involves mounting the electrode to a mandrel, filling the
spaces between the edges (26) of the electrode with a polymer and
then removing the resulting tubular structure from the mandrel. The
cooling fluid can pass through a hollow spiral electrode (58) for
enhanced cooling effectiveness.
Inventors: |
Maguire; Mark A. (San Jose,
CA), Li; Hong (Cupertino, CA), Karratt; Joseph M.
(Sunnyvale, CA), Valencia; Aurelio (East Palo Alto, CA) |
Assignee: |
Medtronic, Inc. (Minneapolis,
MI)
|
Family
ID: |
25163727 |
Appl.
No.: |
08/794,803 |
Filed: |
February 4, 1997 |
Current U.S.
Class: |
606/41;
607/122 |
Current CPC
Class: |
A61B
18/1492 (20130101); A61B 2218/002 (20130101); A61B
2018/00357 (20130101); A61B 2018/00011 (20130101); A61B
2018/00029 (20130101); A61B 17/12022 (20130101); A61B
2018/00577 (20130101); A61B 2018/00023 (20130101) |
Current International
Class: |
A61B
18/14 (20060101); A61B 17/12 (20060101); A61B
18/00 (20060101); A61N 001/05 () |
Field of
Search: |
;606/27,28,29,32,33,41,46 ;600/373,374,381 ;607/119,122 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0608 609 A2 |
|
Aug 1994 |
|
EP |
|
96/39966 |
|
Dec 1996 |
|
WO |
|
Primary Examiner: Jastrzab; Jeffrey R.
Assistant Examiner: Ruddy; David M.
Attorney, Agent or Firm: Townsend and Townsend and Crew
LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. patent application Ser. No.
08/794,840, entitled "Systems and Methods for Tissue Mapping and
Ablation," (Attorney Docket 14875-002700), and U.S. patent
application Ser. No. 08/794,066, entitled "Linear Ablation
Catheter," (Attorney Docket 14875-003100), both filed on the same
day as this application and both assigned to the same assignee, the
disclosures of which are incorporated by reference.
Claims
What is claimed is:
1. An ablation catheter assembly comprising:
a handle;
a catheter shaft extending from the handle;
the catheter shaft comprising a tip portion with a fluid passage
and a distal end;
at least one spiral tubular ablation electrode circumscribing the
tip portion;
the at least one spiral tubular ablation electrode having a fluid
entrance and a fluid exit and defining a fluid flow path
therebetween; and
said fluid entrance fluidly coupled to said fluid passage so that a
fluid passing through said fluid passage can enter and flow through
said at least one spiral tubular electrode in a spiral path.
2. The catheter according to claim 1 wherein said fluid passage has
a cooling fluid entrance to provide a cooling fluid to said passage
and into said at least one spiral tubular electrode.
3. The catheter according to claim 1 wherein said at least one
spiral tubular ablation electrode comprises a plurality of
spaced-apart tubular spiral electrodes.
4. The catheter according to claim 1 wherein said at least one
spiral tubular ablation electrode has a circular cross-sectional
shape.
5. The catheter according to claim 1 wherein said at least one
spiral tubular ablation electrode is spaced apart from the distal
end.
6. The catheter according to claim 1 wherein said fluid exit opens
into a region external of said catheter shaft.
7. The catheter according to claim 1 wherein said at least one
spiral tubular ablation electrode comprises a plurality of said
fluid exits.
8. The catheter according to claim 1 wherein said at least one
spiral tubular ablation electrode comprises one said fluid
entrance.
9. The catheter according to claim 1 wherein said at least one
spiral tubular ablation electrode comprises one said fluid
exit.
10. An ablation catheter assembly comprising:
a handle;
a catheter shaft extending from the handle;
the catheter shaft comprising a tip portion with a fluid passage
and a distal end;
the tip portion further comprising at least one linear ablation
electrode spaced-apart from the distal end;
said at least one linear ablation electrode comprising outer and
inner surfaces;
said inner surface being effectively fluidly exposed to said fluid
passage so that a cooling fluid passing through said fluid passage
effectively directly contacts said inner surface to cool the at
least one linear ablation electrode; and
said tip portion comprising inner and outer tubular members
defining said fluid passage therebetween, said fluid passage
comprising an entrance, an exit, and a pressure-sensitive portion
which opens only when the fluid pressure at the entrance of said
fluid passage exceeds a chosen level so the cooling fluid can pass
along the fluid passage from the entrance to the exit.
11. The catheter according to claim 10 wherein said at least one
linear ablation electrode comprises a plurality of spaced-apart
band electrodes.
12. The catheter according to claim 11 wherein at least one of said
band electrodes is circular.
13. The catheter according to claim 11 wherein at least one of said
band electrodes is semicircular.
14. The catheter according to claim 10 wherein said at least one
linear ablation electrode comprises a plurality of spiral
electrode.
15. The catheter according to claim 10 wherein said entire inner
surface of said at least one linear ablation electrode is exposed
to said fluid passage.
16. The catheter according to claim 10 wherein at least portions of
said inner surface of said electrode are exposed to said fluid
passage.
17. The catheter according to claim 10 further comprising a liquid
permeable porous material covering said inner surface.
18. The catheter according to claim 10 wherein the inner surface is
a bare surface exposed directly to said fluid passage.
19. The catheter according to claim 10 wherein the fluid passage
comprises a plurality of said exits.
20. A method for cooling at least one spiral ablation electrode of
an ablation catheter assembly comprising:
positioning a tip portion of a catheter shaft of an ablation
catheter assembly at a target site of a body organ;
flowing cooling fluid through said at least one spiral tubular
ablation electrode along a spiral path thereby cooling said at
least one spiral tubular ablation electrode;
whereby an improved lesion can be created by said ablation catheter
assembly due to the efficient cooling of the tubular ablation
electrode, thereby allowing energy to be delivered by the electrode
at a higher power levels for a longer duration.
21. The method according to claim 20 whereby said at least one
spiral tubular ablation electrode creates a plurality of lesions
which join one another to form said improved lesion.
22. The method according to claim 20 wherein said positioning step
is carried out with the target site being within a heart of a
patient.
23. The method according to claim 20 wherein said flowing step is
carried out using chilled saline as the cooling fluid.
24. The method according to claim 20 wherein the flowing step is
carried out using at least one spiral tubular ablation electrode
which is spaced apart from the distal end of the tip portion.
25. The method according to claim 20 wherein said flowing step is
carried out by flowing cooling fluid through a plurality of spiral
tubular ablation electrodes.
26. The method according to claim 20 wherein said flowing step is
carried out by flowing cooling fluid through a perforated spiral
tubular ablation electrode.
Description
BACKGROUND OF THE INVENTION
Catheter assemblies are often used to ablate surface tissue within
a heart. The catheter assembly typically includes a handle and a
catheter shaft extending from the handle, the catheter shaft having
a tip portion. The tip portion typically includes a tip ablation
electrode at the distal end and a linear ablation electrode along
the tip portion spaced apart from the tip electrode. The linear
ablation electrode is typically a series of circular band
electrodes, one or more spiral electrodes or one or more braided
electrodes. While it is desirable to ablate tissue at the target
site, it is not desirable to overheat the tissue, or the blood in
the vicinity of a target site, because blood can desiccate causing
coagulum.
SUMMARY OF THE INVENTION
The present invention is directed to an ablation catheter assembly
in which one or more linear ablation electrodes extending along the
catheter shaft are cooled by permitting cooling fluid, typically
saline, to effectively directly contact the inner surface of the
linear ablation electrodes.
The fluid cooled ablation catheter assembly includes a catheter
shaft having a tip portion with a hollow interior, defining a fluid
passage, and a distal end. The tip portion also has a linear
ablation electrode spaced apart from the distal end. The linear
electrode has an inner surface which is effectively fluidly exposed
to the fluid passage of the tip portion so that a cooling fluid
passing through the fluid passage effectively directly contacts the
inner surface so to efficiently cool the linear electrode. A
primary advantage of the invention is that it permits electrodes at
other than the tip of the catheter to be efficiently cooled using a
cooling fluid.
The inner surface of the linear electrode is effectively fluidly
exposed to the cooling fluid in two basic ways. First, the inner
surface of the linear electrode can be an uncoated, bare surface so
the cooling fluid wets the bare surface. This can occur by having
all or part of the inner surface directly or indirectly fluidly
coupled to the fluid passage of the tip portion. It can also occur
if all or part of the inner surface of the linear electrode is
covered by a porous material which allows the cooling fluid to
contact the bare inner surface of the linear electrode. Second, the
inner surface can be covered by a material which prevents direct
contact by the cooling fluid with a bare inner surface of the
linear electrode; in this event the material must be such to not
impede heat transfer between the inner surface of the linear
electrode and the cooling fluid to any significant extent. Such a
material would preferably have a thermal conductivity adequate to
allow the cooling fluid to maintain an electrode temperature
between about body temperature (37.degree. C.), or slightly below,
and 100.degree. C., but more preferably between about 37.degree. C.
and 70.degree. C. to reduce the risk of blood coagulation. Such a
covering material may be desired or necessary to ensure the
columnar integrity of the catheter shaft is maintained even though
a less-than-optimal bond is typically created between the metal
electrode and the shaft. For example, a thin layer of PTFE,
polyamide or PET, such as 0.0005"-0.002" thick, could be used to
cover the inner surface of the linear electrode and catheter shaft
and not significantly impede heat transfer between the cooling
fluid and the linear electrode. Although these materials may not be
good heat conductors, the thinness of the layer in this example
keeps its thermal insulation properties to a reasonably low value.
Therefore, the cooling fluid is considered to effectively directly
contact the inner surface of the linear ablation electrode when the
heat transfer from the linear electrode to the cooling fluid is
such that the electrode temperature is maintained at the
temperatures discussed above.
One method for making the tip portion of the catheter shaft
involves mounting the electrodes to a mandrel and then filling the
spaces between the edges of the electrodes with a polymer. Other
assembly and construction methods can also be used.
The cooling fluid can be directed out of the catheter at the distal
end of the tip portion. Cooling fluid can also be directed out of
the catheter (into the bloodstream) at locations other than the
distal end. For example, exit holes for fluid egress can be located
on or between individual ablation electrodes.
Alternatively, the cooling fluid can be partly or totally
recirculated, that is directed back up through the catheter shaft
after having passed and cooled the linear electrode. Therefore, the
amount of cooling is not limited by the amount of the cooling
fluid, such as saline, that can be properly or safely injected into
the patient. This recirculation ability is therefore useful when it
is desirable to limit or prevent injection of fluid into the
patient.
Other features and advantages of the invention will appear from the
following description in which the preferred embodiments have been
set forth in detail in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified overall view of a catheter assembly made
according to the invention;
FIG. 2 is an enlarged, simplified cross-sectional view of a section
of the tip portion of the catheter assembly of FIG. 1 using a
series of circumferential band electrodes along the tip portion,
the band electrodes spaced apart from the distal end of the tip
portion;
FIG. 3 is a view similar to FIG. 2 but using semicircular
electrodes;
FIG. 4 is a view similar to FIG. 2 but using a spiral
electrode;
FIG. 5 shows a tip portion including an outer tubular member
similar to the tip portion of FIG. 4 and an inner tubular member
with a series of holes providing fluid access to the inside surface
of the spiral electrode;
FIG. 6 shows a structure similar to that of FIG. 5 but using the
band electrodes of FIG. 2 and having complete circumferential gaps
in the inner tubular member exposing the entire inner surfaces of
the band electrodes;
FIG. 7 illustrates an alternative tip portion showing two spiral
electrodes having circular cross-sectional shapes embedded within
an outer tubular member, the inside surface of the electrodes and
the outer tubular member being covered by a porous liner;
FIG. 7A is a longitudinal cross-sectional view of the tip portion
of FIG. 7;
FIG. 7B is a radial cross-sectional view taken along line 7B--7B of
FIG. 7 showing an inner fluid flow passage defined within the
interior of the tip portion and a fluid impermeable tube also
within the interior and through which various electrical wires and
manipulator elements can pass, the tube not being shown in FIG. 7A
for ease of illustration;
FIG. 7C is an enlarged view of a portion of FIG. 7A illustrating
the exposure of the inside surface of the spiral electrode to the
porous liner;
FIG. 8 is a view similar to FIG. 7B but showing a porous bi-lumen
extrusion within the interior of the tip portion;
FIG. 9 is a longitudinal cross-sectional view of an alternative tip
portion made according to the invention;
FIG. 9A is an enlarged view of a portion of the tip portion of FIG.
9 showing the entrance to the fluid passage;
FIG. 9B illustrates the tip portion of FIG. 9 during fluid flow
through the fluid passage;
FIG. 9C is an enlarged view of a portion of the tip portion of FIG.
9B illustrating passage of the cooling fluid into the fluid
passage;
FIG. 10 is a view similar to FIG. 9 of an alternative embodiment in
which several exits from the fluid passage are positioned along the
length of the tip portion;
FIG. 11 is an overall view of a further embodiment of a catheter
assembly using hollow spiral electrodes;
FIG. 11A is an enlarged view of a part of a tip portion of the
catheter assembly of FIG. 11;
FIG. 11B is a longitudinal cross-sectional view of the tip portion
of FIG. 11A illustrating the flow of cooling fluid through the
spiral electrodes;
FIG. 11C is a cross-sectional view taken along line 11C--11C of
FIG. 11B; and
FIG. 12 is a partial side view of the tip portion of a still
further embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a catheter assembly 2 comprising a handle 4 and
a catheter shaft 6 extending from the handle. Catheter shaft 6
includes a main portion 8 and tip portion 10. Tip portion 10 is, as
is standard, relatively flexible to be maneuverable and placeable
in different configurations by one or more manipulators 12, 13
mounted to body 14 of handle 4. Handle 4 includes an electrical
connector 16 to permit electrical connection with a set of
electrodes 18 carried by tip portion 10. Electrodes 18 are
ablation-capable electrodes. Electrodes 18 are used to create
linear lesions and are sometimes collectively referred to herein as
a linear ablation electrode or a linear electrode. These various
components discussed above with reference to FIG. 1 are generally
conventional. See, for example, U.S. Pat. No. 5,487,757, entitled
"Multicurved Deflectable Catheter" and U.S. patent application Ser.
No. 08/613,298, filed Mar. 11, 1996, entitled "Method and Apparatus
for RF Ablation", the disclosures of which are incorporated by
reference. Handle 4 also has a fluid port 21 which permits saline,
or another cooling fluid, to be directed through catheter shaft 6
to cool electrodes 18 as discussed below.
FIGS. 2-6 are simplified views and do not show various elements,
such as radial deflection manipulator wires, lateral deflection
core wires, thermocouple wires, electrical power wires, etc., for
ease of illustration.
FIG. 2 illustrates an enlarged simplified sectional view of a
section of tip portion 10 including two band electrodes 18. Tip
portion 10 is seen to include alternating lengths of band
electrodes 18 and polymer sections 24 made of polyurethane or other
suitable materials. Electrodes 18 of the embodiment of FIG. 2 may
have the smooth sides indicated only if a sufficiently strong bond
can be created between metal electrodes 18 and polymer sections 24.
It may, however, be necessary to provide mechanical interlocking
features which enhance the connection between electrodes 18 and
sections 24.
Band electrodes 18 are typically made of platinum-iridium or
stainless steel. In this way the inside surfaces 28 of band
electrodes 18 are fully exposed to the interior 30 of tip portion
10. The provision of cooling fluid 32, typically saline, along
interior 30 allows the cooling fluid to directly contact inside
surface 28 of band electrodes 18 thus efficiently cooling the band
electrodes during ablation procedures. Cooling fluid 32 passes
through interior 30 and out an exit opening 33 adjacent to tip
portion 10.
FIG. 3 illustrates an alternative embodiment of the invention
similar to FIG. 2. However, instead of circumferential band
electrodes 18, semicircular band electrodes 34 are used as the
linear ablation electrode with tip portion 10a. This is to allow
more cross-sectional area to be comprised of catheter shaft
material to maintain adequate structural support.
FIG. 4 is an embodiment similar to FIG. 2 and shows a tip portion
10b using one or more spiral electrodes 36 as the linear ablation
electrode.
FIG. 5 illustrates a tip portion 10c comprising an outer tubular
member 38 similar in construction to tip portion 10b and an inner
tubular member 40. Inner tubular member 40 is made of a polymer
material, such as polyurethane, silicone, PET or polyimide, and has
a series of holes 42 therein. Holes 42 are positioned to be aligned
with the inner surface 28 of spiral electrodes 36. In this way the
interior 30c of tip portion 10c is in fluid communication with the
inside surface 28 of spiral electrodes 36 to permit cooling saline
32 to contact inner surface 28 of spiral electrodes 36.
Inner tubular member 40 could be replaced by a braided tubular
structure to provide uniform shaft support for the electrodes; such
a braided or other woven tubular structure would have numerous and
substantial openings so the cooling fluid can contact the inside
surfaces of the electrodes.
FIG. 6 illustrates an alternative to the embodiment shown in FIG.
5. In FIG. 6 tip portion 10d includes an outer tubular member 38d
similar to tip portion 10 of FIG. 2 and an inner tubular member 40d
similar to inner tubular member 40 of FIG. 5. However, inner
tubular member 40d has circumferentially extending cutouts 44
aligned with each band electrode 18 to permit all or a substantial
part of inside surface 28 to be contacted by cooling saline 32, as
opposed to the situation of FIG. 5 in which only a portion of the
inside surface 28 is directly exposed to the cooling saline 32.
Tip portion 10 can be made by mounting or forming band electrodes
18 on a mandrel, and then filling the region between the lateral
edges 26 of the band electrodes with a suitable polymer to create
the tubular structure illustrated in FIG. 2. After curing, tip
portion 10 is mounted to the distal-most polymer section 24 in a
conventional manner, typically through the use of an adhesive or
heat welding.
The construction of tip portion 10c could proceed generally as
follows. A tubular member 40 is formed with holes 42 and then
mounted on a mandrel. Spiral electrode 36 is then wound about inner
tubular member 40 covering holes 42. A suitable thermoplastic
polymer or thermoset material, such as silicone, is then introduced
between opposed lateral sides 26b of spiral electrode 36 so to fill
the space between the sides. When sufficiently cured, the structure
is then removed from the mandrel and a tip electrode 20 can be
mounted in a conventional fashion.
The above embodiments have been described on the basis that tip
portion 10 has an exit opening 33 adjacent tip portion 10; see FIG.
1. This type of fluid flow, in which the cooling fluid, typically
saline, exit adjacent or through the tip portion, is shown in U.S.
Pat. No. 5,348,554, entitled "Catheter for RF Ablation with Cooled
Electrode", and U.S. Pat. No. 5,462,521, entitled "Fluid Cooled and
Perfused Tip for a Catheter", the disclosures of which are
incorporated by reference. U.S. Pat. No. 5,348,554 also illustrates
a catheter having a cooling fluid return passageway so that cooling
fluid, after reaching the distal end of the tip section of the
catheter, can be returned to the source so that the cooling fluid
does not flow into the body but rather recirculates. Parallel
conduit, recirculating systems can be used with the present
invention. A system could also be devised in which part of the
cooling fluid was directed out of the tip portion of the catheter
shaft and part recirculated; fluid could also be directed out of
the catheter at or between each electrode.
In use, tip portion 10 is located at the appropriate target site
using manipulators 12 on handle 4. When in position, appropriate
energy is applied to the ablation electrodes, such as band
electrodes 18 or spiral electrodes 36, to ablate the tissue. During
ablation, coolant, typically saline 32, is passed through port 21,
through catheter shaft 6 and into interior 30 of tip portion 10
where the saline comes into direct physical contact with inner
surface 28 of the ablation electrodes so to cool the ablation
electrodes. This helps to reduce overheating in the vicinity of
ablation electrodes 18, 36 thus helping to eliminate undesirable
consequences of overheating, such as the excessive coagulation of
blood and the unintended destruction of healthy tissue adjacent to
the target site. The efficient cooling of the linear ablation
electrode permits longer lesions to be created by permitting higher
RF powers without resulting in excessive electrode heating. The
lesions will be deeper into the tissue and will tend to flow into
one another, that is join up, to create a linear lesion when using
spaced-apart band or spiral electrodes. Cooling fluid, such as
saline 32, can also be permitted to pass out of tip portion, such
as through opening 33 adjacent to tip 20, or through other openings
formed, for example, adjacent or through each band electrode 18;
alternatively, some or all of the cooling fluid could be caused to
recirculate and not be expulsed from tip portion 10.
It is known to cool a tip electrode and apply the cooled tip
electrode to a target site while monitoring the heart to see if
cooling the target site has a positive affect on arrhythmia; if it
does then the tissue at the target site is ablated. The invention
can also be used to test for the expected effectiveness of creating
a linear lesion at a target site. To do so tip portion is
positioned so the linear ablation electrode is at the target site
and the linear electrode is cooled by the cooling fluid to chill
the tissue sufficiently to create what is sometimes called a test
lesion. If chilling the tissue at the target site affects
arrhythmia in a positive way, energy is supplied to the linear
ablation electrode to ablate the tissue and create a linear lesion
at the target site.
FIGS. 7-7C illustrate alternative tip portion 10e comprising a
plurality of spiral electrodes 44 having circular cross-sectional
shapes. Electrodes 44 are embedded within and carried by outer
tubular member 38e. The inside surfaces 28e, see FIG. 7C, of spiral
electrodes 44 and the inside surface 46 of outer tubular member 38e
are covered by a porous inner tubular member 40e.
Porous inner tubular member 40e is preferably a silicone,
polyolefin, or other suitable porous material about 0.001"-0.010"
thick, more preferably about 0.003"-0.008" thick, to provide fluid
access to the inner surface 28e of electrodes 44 while providing
some structural support to tip portion 10e. FIG. 7B illustrates a
liquid impervious tube 48 extending along the interior 30e of tip
portion 10e. Tube 48 is used to guide various wires and other
components along tip portion 10e and keep those components from
being exposed to cooling fluid 32. In the embodiment of FIGS. 7-7C
cooling fluid 32 exits tip portion 10e through an axial hole 49
formed in tip portion 10e. Alternatively, an additional tube,
similar to tube 48, could be used to direct cooling fluid 32 in a
reverse fluid flow along tip portion 10e.
FIG. 8 illustrates a cross-sectional view similar to that of FIG.
7B but using a porous bi-lumen extrusion as the inner tubular
member 40f. Inner tubular member 40f divides interior 30f into a
main region 50, through which cooling fluid 32 flows, and a
supplemental region 52 housing tube 48, tube 48 serving the same
purpose as in the embodiment of FIGS. 7-7C. Extrusion 40f may be
made of a suitable porous material such as polyethylene, polyolefin
or silicone.
FIGS. 9-9C illustrate a further embodiment of the invention in
which a tip portion 10g has a radially expandable outer tubular
member 38g. Member 38g includes a silicone layer 54 which dilates
to define fluid passage 30g, see FIG. 9C, between silicone layer 54
and inner tubular member 40g. This dilation occurs when cooling
fluid 32 is supplied at a sufficiently high pressure at the
entrance 56 to fluid passage 30g to cause the cooling fluid to flow
along the dilated passage 30g and exit tip portion 10g at exit
openings 33g. Silicone layer 54 is sufficiently thin, such as
0.0005" to 0.002" thick, so that cooling fluid 32 need not actually
contact the inside surfaces of electrodes 44 to effectively cool
the electrodes. Alternatively, silicone layer 54 can be a porous
silicone to provide actual direct contact of the cooling fluid with
the inside surfaces of electrodes 44.
FIG. 10 illustrates a tip portion 10h similar to tip portion 10g
but having a number of exits 33h along the tip portion. This can be
useful because it not only causes convective cooling of the
electrodes, but causes the cooling fluid to also directly cool or
"bathe" the issue being ablated.
FIGS. 11-11C illustrate a further embodiment of the invention in
which a tip portion 10i has a plurality of tubular spiral
electrodes 58. Electrodes 58 are preferably stainless steel
hypotubes having an outside diameter of about 0.014" and an inside
diameter of about 0.010". Proximal end 60 of each tubular electrode
58 opens into region 50 defined within inner tubular member 40h and
through which cooling fluid 32 flows. Cooling fluid flows into
proximal end 60, through the interior of tubular spiral electrode
58 and out through the distal end 62 of the spiral electrode. In
this embodiment the inside surface of spiral electrode 58
corresponds to inside surface 28 of the electrodes in the other
embodiments and permits direct cooling contact of the cooling fluid
with the electrode. Although in this embodiment each electrode 58
has a single entrance and a single exit, each spiral electrode
could have one or more entrances and one or more exits. For
example, distal ends 62 could be blocked and spiral electrodes 58
could have numerous small openings 64, see FIG. 12, through which
cooling fluid could flow out of tip portion 10j. The sizes of the
small openings could be chosen to ensure generally equal or unequal
flow rates through the openings.
Other modifications and variation can be made to the disclosed
embodiments without departing from the subject of the invention as
defined in the following claims. For example, the invention could
be constructed to ablate other than cardiac tissue, such as the
prostate, the uterus, cancer tumors, or coronary artery blockages
(plaques). Temperature sensors may be used to measure the
temperature at the tissue interface; to do so temperature sensors
should be positioned to provide the most accurate temperature
measurements, typically positioned spaced-apart from the
fluid-cooled electrodes. To increase the ID/OD ratio for the hollow
coil design of FIGS. 7-12, the hollow coil could have a flattened,
rather than circular, cross-sectional shape. This smaller profile
electrode would allow a smaller shaft OD or a larger shaft ID for
catheter shaft components, such as fluid lumen, manipulator
wire(s), electrical wires, etc.
* * * * *